/*
 * Copyright (C) 2008 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package cn.com.dhc.danlu.util;

import android.os.Handler;
import android.os.Message;
import android.os.SystemClock;

/**
 * Schedule a countdown until a time in the future, with
 * regular notifications on intervals along the way.
 *
 * Example of showing a 30 second countdown in a text field:
 *
 * <pre class="prettyprint">
 * new CountDownTimer(30000, 1000) {
 *
 * public void onTick(long millisUntilFinished) {
 * mTextField.setText("seconds remaining: " + millisUntilFinished / 1000);
 * }
 *
 * public void onFinish() {
 * mTextField.setText("done!");
 * }
 * }.start();
 * </pre>
 *
 * The calls to {@link #onTick(long)} are synchronized to this object so that
 * one call to {@link #onTick(long)} won't ever occur before the previous
 * callback is complete.  This is only relevant when the implementation of
 * {@link #onTick(long)} takes an amount of time to execute that is significant
 * compared to the countdown interval.
 */
public abstract class CountDownTimer {
    private static final int MSG = 1;
    /**
     * Millis since epoch when alarm should stop.
     */
    private final long mMillisInFuture;
    /**
     * The interval in millis that the user receives callbacks
     */
    private final long mCountdownInterval;
    private long mStopTimeInFuture;
    /**
     * boolean representing if the timer was cancelled
     */
    private boolean mCancelled = false;

    private Handler mHandler = new Handler () {
        @Override
        public void handleMessage (Message msg) {

            synchronized (CountDownTimer.this) {
                if (mCancelled) {
                    return;
                }

                final long millisLeft = mStopTimeInFuture - SystemClock.elapsedRealtime ();

                if (millisLeft <= 0) {
                    onFinish ();
                } else if (millisLeft < mCountdownInterval) {
                    // no tick, just delay until done
                    sendMessageDelayed (obtainMessage (MSG), millisLeft);
                } else {
                    long lastTickStart = SystemClock.elapsedRealtime ();
                    onTick (millisLeft);
                    // take into account user's onTick taking time to execute
                    long delay = lastTickStart + mCountdownInterval - SystemClock.elapsedRealtime ();
                    // special case: user's onTick took more than interval to
                    // complete, skip to next interval
                    while (delay < 0) {
                        delay += mCountdownInterval;
                    }
                    sendMessageDelayed (obtainMessage (MSG), delay);
                }
            }
        }
    };

    /**
     * @param millisInFuture
     *         The number of millis in the future from the call
     *         to {@link #start()} until the countdown is done and {@link #onFinish()}
     *         is called.
     * @param countDownInterval
     *         The interval along the way to receive
     *         {@link #onTick(long)} callbacks.
     */
    protected CountDownTimer (long millisInFuture, long countDownInterval) {
        mMillisInFuture = millisInFuture;
        mCountdownInterval = countDownInterval;
    }

    /**
     * Cancel the countdown.
     */
    public synchronized final void cancel () {
        mCancelled = true;
        mHandler.removeMessages (MSG);
    }

    /**
     * Start the countdown.
     */
    public synchronized final CountDownTimer start () {
        mCancelled = false;
        if (mMillisInFuture <= 0) {
            onFinish ();
            return this;
        }
        mStopTimeInFuture = SystemClock.elapsedRealtime () + mMillisInFuture;
        mHandler.sendMessage (mHandler.obtainMessage (MSG));
        return this;
    }

    /**
     * Callback fired on regular interval.
     *
     * @param millisUntilFinished
     *         The amount of time until finished.
     */
    public abstract void onTick (long millisUntilFinished);

    /**
     * Callback fired when the time is up.
     */
    public abstract void onFinish ();
}